Abstract: In order to study the mechanism of the oxidative leaching of marmatite, the slurry of synthetic marmatite was selected as the research object. The electrochemical behavior of marmatite in sulfuric acid leaching was investigated by the three-electrode method. The experimental results proved the intermediate product of H₂S in the leaching of marmatite. The results also showed that oxygen, element sulfur disperser as well as chloride ions could accelerate the electrochemical oxidation of marmatite in sulfuric acid. The electrochemical oxidation of sphalerite was retarded but that of marmatite was promoted with the increase of acidity. Marmatite was much easier to be oxidized through electrochemistry than sphalerite. The electrochemical oxidation of marmatite should not be neglected in the sulfuric acid leaching.